Methods of igniting a gas air-burner utilizing pelletized phosphorus



c. DE PRIESTER METHODS OF I NITING A GAS AIR-BURNER.

G UTILIZING PELLETIZED PHOSPHORUS' Aug. 12, 1958 Filed Sept 20, 1955 mM. E s R m a 0% m T JU- N E m .a m NL T M A G G w I l c F F. Y B

FIG.2

United States Patent METHODS OF IGNITING A GAS AIR-BURNER UTILIZINGPELLETIZED PHOSPHORUS Coral L. De Priester, Fullerton, Califi, assignorto California Research Corporation, San Francisco, Calif., a corporationof Delaware Application September 20, 1955, Serial No. 535,462

2 Claims. (Cl. 166-89) This invention relates to methods of generatingheat in subterranean formations penetrated by a wellbore and relatesmore specifically to methods for generating such heat to ignite downholegas-air burners.

The use of downhole gas-air burners for well stimulation and forinitiating underground combustion drive in secondary recovery operationis becoming increasingly common in the petroleum industry, and the useof such devices offers a number of advantages over other ignition andwell stimulation methods and systems. Such burners usually are disposedadjacent the formation to be treated and are supplied from the surfacewith a mixture of fuel gas and an oxygen-containing gas. A number ofignition methods have been proposed for such burners, but so far as I amaware none of such proposed systems have been entirely satisfactory.Some of such burners are ignited by electrical means such as an electricheating coil or a spark plug disposed in or adjacent the burnercombustion chamber and energized from the surface to produce therequired temperature for ignition. However, such systems have thedisadvantage that they require an electrical conduit from the surface tothe burner location, thus increasing the complexity and cost of theburner installation and increasing the possibility of malfunctioningthrough failure of the electrical conduit. The use of such systems hasthe additional disadvantage that the electrical igniting units oftenfail, owing to the elevated temperature to which they are exposedadjacent the burner, and this failure usually necessitates theremoval ofthe entire burner assembly from the well bore for replacement or repair.

Numerous chemical methods have been proposed for igniting downholegas-air burners or for otherwise providing an elevated temperature in awell bore. One proposed system for heating the well bore and contactingthe formation with alkali metal hydroxides utilizes sodium or potassiumcapsulated in a suitable watersoluble material and injected into thewell bore. Water is then injected into the well bore to dissolve thecapsulating material and react with the sodium or potassium to producethe desired exothermic reaction. However, this system is not suitablefor burner ignition owing to the fact that heat is released from thereaction at a high er rate than can be utilized, resulting in aviolent'reaction and expulsion of the unreacted sodium from "the burnerprior to ignition of the gas-air mixture. This system has the furtherdisadvantage of requiring the injection of water into the formation todissolve the watersoluble coating, thus creating the possibility ofproducing water blocking of the treated formation.

Broadly the present invention contemplates the use of a pellet ofelemental phosphorus encased in an inert solid having a melting pointbelow the temperature at the burner location. The pellet is injectedinto the formation through tubing running from the surface to theburner, and is lodged in a position in the burner to produce ignition.The flow of the gaseous combustible mixture over the pellet produces orhastens melting of exposure of the elemental phosphorus to the passinggaseous combustible mixture the phosphorus reacts with the oxygen .inthe mixture, is ignited and subsequently ignites the gaseous combustiblemixture.

It is therefore an object of the present invention to provide improvedmethods and apparatus for igniting downhole gas-air burners.

It is an additional object of the present invention to provide methodsof igniting a downhole gas-air burner utilizing the delivery to theburner location of selected chemicals capable of producing an exothermicreaction.

It is a further object of the present invention to pro-1 vide methodsfor igniting a downhole gas-air bnrnerin which a selected chemicalcapable of producing an exothermic reaction is delivered to the burnerto produce ignition without requiring the injection of extraneous ma.-terials into the well bore.

It is a further object of the present invention to pro. vide methods ofigniting a downhole gas-air burner by exothermic chemical reaction suchthat no residue from the reaction .or delivery process remains in theburner. system. a

It is an additional object of the present invention to provide methodsof ignitinga downhole gas-air burner. which do not require the use ofelectrical cables or wire.- lines from the earths surface to the burnerlocation;

I It is a further object of the present invention to provide methods ofigniting downhole gas air burners utiliz-- ing a pellet comprisingelemental phosphorusencased in. an inert solid having a melting pointbelow the tem-- perature existing at the burner location. 1

It is a further object of the present invention to provide a method ofigniting a downhole gas-air burner utilizing. a pellet comprisingelemental phosphorus encased in ice; in which the pellet is delivered tothe burner location and.- the encasing ice melted to expose theelemental phosphorus to the passing gaseous combustible mixture. v

Objects and advantagesother than thoseset forth above will be apparentfrom the following description when read in connection with theaccompanying drawing, in which:

Fig. 1 illustrates a representative pellet suitable for use in thepresent invention in connection'with a' portion of valving associatedtherewith;

Fig. 2 illustrates the disposition of representative equip-1 ment in awell bore for carrying out the methodof-the present invention; and

Fig. 3 illustrates a device for retaining apellet: in a predeterminedposition in the combustion chamber;

Referring more particularly to the. drawing .by characterv of reference,Fig. 1 illustrates the disposition of a repre-'v sentative pellet of thepresent invention in aportion ofthe delivery assembly. As shown in .Fig.11, referencecharacter 11 designates particlessofelemental-phosphorusencased in a suitable solid material 12to form a pellet 13. Material 12may be any suitable material which is inert" to the elemental phosphorusand which'has a melt-ing; point below the temperature at the locationofthe burner. 1 Suitable inert materials include benzene, tridecanerand';triethylene glycol. Additionally, I have found that water is aparticularly desirable inert material to use, since it is economical andeaily solidified. Pellet 13 may be formed in a mold or any othersuitable means to form 16 and tubing 20 are connected at their lowerends to aeui'ta'ble' gas' air'burner shown diagrammatically a's21. Thecombustible mixture is supplied to the burner through the annulusbetween tubing 16 and tubing-20. Burner 21 may comprise a combustionchamber portion 22 into which conduit 16 leads and in which thecombustion occurs. Combustion chamber 22 is preferably terminated at'itslower end by restricting passage 23 having a diameter less than theminor dimension of pellet 13. Burner 21 may further comprise a conicalexhaust portion 24 for'directing the combustion products from combustionchamber" 22 into contact with the formation and/or the fluid in the wellbore. A gas-air burner having featuressimilar to those illustrated inFig. 2 is disclosed" and claimed in the copending application of C. L.DePri'ester and C. N. 'Simm, Serial No. 525,505, filed August 1, 195.The gaseous combustible mixture to be burned may be of any suitabletype, such as a mixture of natura'l'gas and air,'and such mixture issupplied from suitable source's designated generally as' 25 and 26 tothe annulus between tubing 20 and tubing 16.

Inope'ration of the present invention, pellet 13 is placed in the upperend of tubing 16 by opening valve 17 with valve '18'closed. 'Afterplacing the capsule in the delivery chamber, valve 17 is closed, andvalve 18 is opened to permit pellet 13 to fall freely through tubing 16.If desired, suitable lubricating material may be placed around pellet 13to facilitate its fall through tubing 16, although I 'have found thatwhen ice is used as the encasing material,"'the normal melting of theice in the delivery chamber or tubing provides satisfactory lubrication.

Pellet 1'3 falls freely through tubing 16 to combustion chamber 22 andbecomeslodged in the restricted opening 23 at thelower end of combustionchamber 22. The gas-air'mix'ture may-then be supplied from sources 25and 26 through the annulus between tubing 20 and tubing 16 to combustionchamber 22 to hasten the melting of the encasinghiaterial. When the'encasing material melts s'ufii'ciently to expose the elementalphosphorus particles 11' to the gas-air mixture, oxidation of thephosphorus occurs and produces a sufficiently elevated temperature toignite thegas-air mixture. The gas-air mixture combustion flame thenstabilizes in combustion chamber 22 to produce the desired heatingeffect.

\ In tl'ie embo'diment described in connection with Fig. 2, thepelletlodged in the restricted opening 23 in the lower end of combustionchamber 22, and it was' assumed that the pellet of phosphorus and'icewas completely dissolved so that no debris remained. However, if thenature of the pellet should be such that plugging of the burner couldpossibly result from'debris, the arrangement illustrated in Fig. 3 canbe utilized to prevent such plugging. As shown in Fig. 3 tubing 16 isterminated at its lower end by a basket member 31 having perforations'32 therein. Me'mber'31 is clbsed atits lower end to retain capsule 13therein. Basket member 31 may be positioned in or just above combustionchamber 22 so as to retain pellet13 in this location after it is droppedthrough tubing 16. Pellet 13 dissolves as before, and the phosphorus isoxidi'zed by the gas-air mixture to produce therequired ignitiontemperature. Any undissolved matter of aparticle size larger thanperforation 32 is retained in the basket member-31 so that no pluggingof burner orifices can result.

The method of the present invention was tested under simulated downholeconditions using injection apparatus similar to that shown in thedrawing. A %-1HCh diameter pellet was formed by freezing phosphorus inwater in a copper mold surrounded by Dry Ice. The pellet was injectedthrough 0.824-inch I. D. tubing a distance of approximately six feetinto thecombustion chamber of a gas-air burner submerged in'water. Waterwas utilized in these particularexperiments-rather than crude oil, butthe nature of themedium surrounding the burner is immaterial to thepresent process. A gas-air mixture was then supplied through the annulusbetween the tubing to the burner, and this mixture was successfullyignited a number of 'ti'mesi In connection'with these experiments, theeffects of pressure-and temperature on the reaction of phosphorus withoxygen were investigated to some extent, and it was found that at atemperature of 70 F. and above, the desired reaction proceededsatisfactorily under pressures ranging from one atmosphere to p. s. 1.g.

It will' be seen that the method of the present invention does notrequire the introduction of anyextraneous materials such as water orother chemicals into the well bore oi burner to dissolve the encasingmaterial, and further," there is no debris remaining from the pellet,since thepho's'pho'rus'will be substantially consumed by oxidation andthe encasing 'material will be blended in with the other'well b'orefluids. Further, the ignition method of thejpresent'invention may easilybe repeated anyde'sired numberof times until the required ignitiono'c'curs.

Although but a fewembodiin'ents' of the presentinvention'have'been'described, it will be apparent to those skilled in'th'e' art that various' changes and modifications may be madethereinwithou't departing from the spirit of"the invention or the scopeof the appended claims.

1; The rnethodof igniting a downhole gas-air burner comprising the stepsof introducing into said burner a'pellet comprising elemental phosphorussurrounded by ice, said ice melting in said burner to expose saidphosphorus, and supplying a gaseousfcombustible, oxygencontainingmixtureto' said burner for oxidizing said' exposed phosphorusto'producea temperature sufiicient to ignite said combustible mixture.

2. The method of igniting a downhole gas-air burner connected to thesurface of the earth through a length of tubing'comprisingthe' stepsof'inj'ecting a pellet through said tubing to position said pelletadjacent'said burner, said pellet comprising elemental phosphorussurrounded by ice; said ice melting atthe temperature existing at thelocation of said burner to expose said phosphorus, and

supplying a gaseous combustible, oxygen-containing mix- 1,278,217 Reid-'Sept.'10, 1918 2,188,737 I-IiXOH Jan. '30; 1940 2,558,726 Barker July3, 1951 2,630,307 Martin Mar. 3, 1953 L 2,747,672 Simm May 29,1956

1. METHOD OF IGNITING A DOWNHOLE GAS-AIR BURNER COMPRISING THE STEPS OFINTRODUCING INTO SAID BURNER A PELLET COMPRISING ELEMENTAL PHOSPHORUSSURROUNDED BY ICE, SAID ICE MELTING IN SAID BURNER TO EXPOSE SAIDPHOSPHORUS, AND SUPPLYING A GASEOUS, COMBUSTIBLE OXYGENCONTAININGMIXTURE TO SAID BURNER FOR OXIDIZING SAID EX-